1. Field of the Invention
The present invention relates to a quality evaluation method of a grown single crystal ingot, and more particularly to such a method, in which components (X factor) influencing the quality of a single crystal ingot monitored in a growing process thereof are selected and then a sampling rule capable of more reasonably and scientifically determining cropping and sampling positions of the single crystal ingot is established based on the integral comparison/analysis of the X factor to thereby minimize the amount of excessive inspections and useless primes, and in which the cropping and sampling operations of the ingot is implemented by an automated system, and the ingot cropping and sampling positions are objectively calculated and databased, so that productivity and efficiency can be maximized.
2. Description of the Prior Art
Silicon Wafers, etc. used as a substrate material for the fabrication of electronic devices such as semiconductors are obtained by slicing a single crystal silicon ingot in thin. A single crystal ingot is produced by forming polycrystalline silicon into a cylindrical single crystal body through Czochralski method (hereinafter referred to as “CZ method”) or Float Zone method (hereinafter referred to as “FZ method”), machining the outer surface of the single crystal body such that the body has a uniform diameter, and cutting the single crystal body to have a predetermined length. The CZ method for forming a single crystal will now be described in brief.
In the CZ method, first, a seed crystal is dipped into a polycrystalline silicon melt solution, and then pulled up to grow an thin elongated crystal from the seed crystal, which is called necking. Then, shouldering for growing the thin elongated single crystal in a diametrical direction perpendicular to the seed crystal pulling direction is performed such that the grown single crystal has a diameter equal to or greater than a predetermined diameter. The shouldered single crystal is grown successively, forming a body that will be formed into wafers. After the single crystal body is grown to a predetermined length, tailing is performed so that the single crystal body is reduced in diameter and then separated from the silicon melt. In this way, the entire process of growing the single crystal ingot is completed.
The grown single crystal body is so cropped as to leave only a body-grown part having a cylindrical shape, and the left cylindrical part is ground at its outer surface to have a predetermined diameter. Then, the cylindrical single crystal body having the predetermined diameter is cut into uniform lengths, by which single crystal ingots with a predetermined length are completely fabricated.
Finally, the single crystal ingot is sliced into wafers of a predetermined thickness by using an inner or outer edge blade or a wire. Then, a series of shaping and polishing processes are performed on such wafers to have properties adequate for the fabrication of semiconductor devices.
However, in the process of growing a single crystal silicon ingot, several process steps such as necking, shouldering, body growing and tailing are performed with the seed crystal contacting the polysilicon melt solution to grow the single crystal silicon ingot into a desired diameter and length. So, various process variables have to be considered when the process is carried out.
Therefore, before the cut body is sliced into thin wafers, the single crystal ingot grown up as above should be cut into a slug to evaluate its quality. That is, it is confirmed whether or not the ingot satisfies quality conditions such as resistivity according to user demand.
Conventionally, the cropping and sampling positions of the single crystal ingot have been determined empirically, for example, the quality evaluation of the single crystal ingot has been generally performed at regular intervals in such a manner that the ingot is cut at equal intervals of, for example, 10 cm to produce slugs or wafers, and the quality of the produced slugs or wafers is evaluated. Accordingly, there has been a problem in that evaluation cost per ingot is expensive too much.